Heat-treated stable-surface alloy steel



May 22, 1923. 1,456,088

P. E. ARMSTRONG HEAT TREATED STABLE SURFACE ALLOY STEEL Filed Dec. 12, 1919 TRANSFORMATION CURVE FOR C 50%, Cr 92, 511 6.50 1, Mn 50%, REST PRI/vc/PALLY Fe zooo [N VEN T OR ATTO EY Patented May 22, 1923.

I'ERGY A. E. ARMSTRONG, F LOUDONVILLE, NEW YORK.

HEAT-TREATED STABLE-SURFACE ALLOY STEEL.

Application filed December 12, 1919. Serial No. 344,294.

To all whom it may concern:

Be it known that I, PERCY A. E. ARM- s'rnoNc, a subject of the King of Great Britain, and a resident of Loudonville, county of Albany, and State of New York, have invented ce'rtain new and useful Improvements in Heat-Treated Stable-Surface Alloy Steel, of which the following is. a specification.

The present application relates to an alloysteel containing rincipally' iron, chromium, silicon and carbon, in such proportions that, when fixed solid solution ground mass by heat-treatment, it is of stable surface character, that is to say, resistant to change or deterioration, such 'as produced in ordinary steel, for example, by staining, oxidizing, corroding and the like agents.

This alloy steel is practically stainless and is resistant to corrosion, oxidation and the like when the ground mass is fixed solld solution by heat-treatment, but is more or less readily attacked by corroding and the like agents when not in such state.

When the ground mass is fixed solid solution by heat treatment, the alloy steel is not attacked orstained to any considerable extent by nitric acid, nor by acetic or other organic acids, fruit juices or the like. It is attacked to some extent, however, by h drochloric acid, sulfu'ric acid and hydro uoric acid, particularly when the acids are diluted.

The heat treatment of this alloy steel may be of various sorts, so long as same resultsin fixin the ground mass of the material substantlall solid solution. For example, the materia may be-heated to a high heat, say about 18501900 F., and cooled rapidly in the air, or quenched in molten salts, oil, water and other suitable quenching agents. The constituents making up the major portion or ground mass of the steel appear to be in solution at about the temperatures stated and to be fixed or rendered solid in such solution by the rapid cooling. Normalizing of the crystalline structure of the material, as by slowly cooling, or by long continued annealing or other equlvalent normalizing treatment, is to be avoided, if the material is to have good stable surface qualities.

The alloy steel -has over about 5% and under about 13% silicon and chromium, taken together, Its stable surface qualities,

treatment, to get desirably good surface stability, cannot be fixed at precisely 13%, but same is at or about the neighborhood of 13% of chromium and silicon, taken together.

The silicon content may be from .5% to 7% and the chromium from 3% to 10%, the proportions being. distributed between the chromium and silicon so as to keep the total of silicon and chromium, taken toether, between .about 5% and about 13%. ith suchproportions of silicon and chromium, taken together, the carbon should be kept low to get good results. Carbon as low as .05% may be used. Preferably the carbon should be kept under one-half of the silicon when taken alone, and under onetenth of silicon and chromium, taken together.

With an alloy steel at about the lower end of the range referred to, containing silicon 2.5% andchromium 3%, for example, the carbon should preferably be under .55%,

since, with such material, further increase of carbon, to say 1%, results in a considerable reduction of the desired surface stabillty in the alloy steel. Carbon .30%, for example, gives good results with these proportions of silicon and chromium, provlded the g'round mass is fixed solid solution by heat treatment.

One good stable surface alloy steel at about the upper end of the range referred to contained silicon 3.7%, chromium 8.9%, carbon '.46%, manganese 23%, sulphur 014%, hosphorus .018% and the remainder iron. ubstantially as ood results ma be obtained with more or ess variation om these figures, using chromium about 8 to 9%, silicon about 3.50 to 4%, and carbon about .40 to .60%.

The proportions given herein are by weight. It is to be noted that the specific gravity of silicon being only about one-half that of chromium or lron, the percentages of this component, when given by volume instead of by weight, are about twice the figures given herein.

My improved alloy steel, containing substantial proportions of sillcon, has greater surface stability, that is to say, is much mo e resis ant to stain, oxidation, corrosion I crease of silicon content alone.

and the like, than similar material not containing a substantial proportion of silicon.

With the use of silicon as described, a substantially homogeneous and readily workable alloy is obtained. The beneficial action of silicon 'is not appreciable where .itis present only in small proportions, say up to about .30.40%'.' To get the beneficial efi'ects desired, at least .50% of silicon must be present, and more silicon is desirable. With the use of silicon as described herein, it becomes possible to have the ground mass of the material substantially solid solution.

The more the ground mass is solid solution bon 11%,, manganese .3% and practically all the remainder iron. The alloysteel may be used in the cast form, if desired, but, when the silicon is under about 5%, it is specially well adapted for mechanical working. It

has a plastic range the length of which is increased with increase of chromium and silicon content, and does not become molten until a temperature is reached above the tem-' perature at which it will subsequently solidi- When cast into small molds it readily solidifies into coherent ingots, which can be worked to good advantage. When cast into larger molds the period of solidification is quite long unless provision is made for Withdrawing the heat fairly rapidly. Pouring rapidly, as, for example, through a large nozzle has been found to be of advantage in casting operations, and this is particularly useful when heat is withdrawn *by permitting the molten metal to stand in the ladle and then pouring at a temperature well down toward the solidification temperature of the metal.

.My improved alloy steel, of course, contains small proportions of metalloids, such as sulphur, phosporus, etc., and may contain variable percentages of metallic elements, substantially all of which may be present, to some extent, at least. If the chromium-silicon content is relatively high. that is to say, in the nei hb'orhood'of 13%,

the proportion of meta ic elements which may be present without substantial detriment to the surface stability of 'the alloy steelmay be correspondingly increased. It

mes es is .undesirable ordinarily with the alloy of ments can be incorporated up to a total of about 2% to 5% without a substantial detriment to the valuable properties of my alloy steel. I may, for example, incorporate with the alloy steel having chromium-silicon content of 13%, as much as 4% of cobalt or nickiel, 1% of manganese, molybdenum, tungsten, vanadium, titanium, zirconium, or other metals which form silicides or compounds or alloys withthe iron, or chromium or both, or which do not materially affect the fixation of solid solution ground mass by heat treatment, with no considerable detriment resulting from their use.

The alloy steel herein described and claimed affords an extremely useful and relatively inexpensive material for making various heat treated products and articles, such as cutlery, tools, etc., which should desirably have good stable surface qualities, but which are not ordinarily to be subjected to the most extreme exposure to staining, oxidizing, corroding and the like agents.

Valves and valve seats for internal combus-' tion engines when made from such material, particularly at about the upper end ofthe chromium and silicon range, stand up over very long periods without regrinding, and the material may be made use of in numerous other ways.

I claim:

1. An alloy steel of substantially high surface stability, having the ground mass fixed substantially solid solution by heat treatment, containing chromium about 3% to 10%, silicon about .5% to 7%, chromium and silicon together about 5% to 13%, carbon over about .05% and under 1/10 of the chromium and silicon taken together, and the principal portion of the remainder iron.

2. An alloy steel of substantially high surface stability when heat treated by heating to about 18501900 F. and cooling, containing chromium about 3% to 10%, silicon about .5% to 7%, chromium and silicon, taken together, about 5% to 13%, carbon about .05% to 1.3%, and the principal part of the remainder iron.

' 3. An alloy steel of substantially high surface stability when cooled down from a high temperature, containin about .5% .and under about chromium over about 3% and under about 10%, silicon and chromium taken together over about 5% and under about 13%, carbon over about ..O5%, and under one-tenth the chromium and silicontaken together, and alsounder one-half the silicon, and the principal part of the remainder iron.

silicon over I 4. An alloy steel of high surface stability when cooled down from a hi h temperature containing silicon about 3. chromium about 8.9%, carbon about .46% and the principal part of the remainder iron.

5. A heat-treated article of substantially highly stable surface character made from alloy steel containing chromium about 8 to 9%, silicon about 3.50 to 4%, carbon about .40.60%, and the principal part of the remainder iron.

6. An article of substantially highly sta- T ble surface character 'made from alloy steel having the ground mass fixed substantially solid solution by heat treatment and containing chromium about 8'to 9%, silicon about 3.50 to 4%, carbon about .40-.60%,

and the principal part of the remainder iron.

7. A cutler article of substantially high- 1y stable sur ace character made from alloy steel having the round mass fixed substantially solid solutlon by heat treatment and containing chromium about 8 to 9%, silicon about 3.50 to 4%, carbon about .40-.60%, and the principal part of the remainder iron.

In testimony that I claim the foregoing, I have hereto set my hand, this 18th day of November, 1919.

PERCY A. E. ARMSTRONG. 

